Effect of inoculum types and microbial community on thermophilic and mesophilic solid-state anaerobic digestion of empty fruit bunches for biogas production

Methane production from solid-state anaerobic digestion (SS-AD) of empty fruit bunches (EFB) using recycling solid-anaerobic digested (S-AD) sludge and liquid-anaerobic digested (L-AD) sludge as inoculum was investigated under thermophilic (55 degrees C) and mesophilic conditions (40 degrees C). The methane production rate of L-AD sludge (2.98-3.27 L-CH4 L-1 reactor d(-1) ) was 1-2 times higher than recycling S-AD sludge (1.36 L-CH 4 L-1 reactor d(-1) ) as inoculum. Methane production of L-AD and S-AD sludge inoculum was 53.5-54.1 and 31.2-39.0 m(3) CH4 tonne(-1) EFB, respectively. The SS-AD of EFB with L-AD and S-AD sludge under thermophilic condition had specific methane activity of 34-96 times higher than the mesophilic condition. Clostridium sp., Methanosaeta sp., and Methanoculleus sp. were responsible for the SS-AD of EFB with L-AD sludge inoculum. The L-AD sludge was suitable inoculum for SS-AD of EFB in terms of methane production rate, cellulose degradation efficiency, biogas production, and microbial activity.